Precision scribing instrument attachment



Aug. 30, 1949. R. s. THOMPSON 2,480,163

PRECISION SCRIBING INSTRUMENT ATTACHMENT Filed April 2, 1946 2Sheets-Sheet l FIG. 5 ID FIG. 6

IN V5 N T017. ROBERT S. THOMPSON Aug. 30, 1949. R. s. THOMPSON PRECISIONSCRIBING INSTRUMENT ATTACHMENT 2 Sheets-Sheet 2 Filed April 2, 1946 FIG.2

FIG.3

FIG.4

IN VE N TOR ROBERT S. THOMPSON FlG.9

A TTORN EY Patented Aug. 30, 1949 PRECISION SCRIBING INSTRUMENTATTACHMENT Robert S. Thompson, Lexington, Ky.

Application April 2, 1946, Serial No. 658,917

(Granted under the act of March ,3, 1883, as amended April 30, 1928;F370 0. G. 757) 7 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

The invention to be hereinafter described relates a precision scribinginstrument attachment.

In the making of optical instruments, as well as in many other fieldsthere is a wide range of uses for precision scribing instruments andattachments requiring a very high degree of accuracy. Among the many maybe cited the tools and equipment for making the grooves, cuts orchannels for the placing of spider-webs forming the cross hairs ininnumerable optical instruments. Unless these webs are extremelyaccurately placed, the instruments in which they are to be used will becorrespondingly faulty. If the metal web-holder of the reticle is notaccurately grooved the difiiculty of placing the web is greatlyincreased with resulting increase in defective instruments.

The main objects of the present invention are to avoid the above andother disadvantages and provide a simple efiicient, compact, durable,accurate, low cost and very quickly and easily applied and adjustedattachment whereby the grooves in the metal frame of a cross hair holdermay be cut with extreme accuracy.

In order to more clearly disclose the construction, operation and use ofthe invention, reference should be had to the accompanying drawingsforming part of the present application. Throughout the several figuresof the drawings like reference characters designate the same parts inthe different views.

In the drawings:

Fig. 1 is a perspective view of the attachment on a milling machine;

Fig. 2 is an enlarged front elevation of the attachment, with tool fullyretracted;

Fig. 3 is a rear elevation;

Fig. 4 is a top plan view; showing in dotted lines the cutter plungerretracted;

Fig. 5 is an end view, looking toward the cutter; Fig. 6 is alongtudinal cross section through bar 2 and associated parts, with theparts in position of Fig. 2;

Fig. '7 is a front elevation of an unprocessed metal cross hair holder;

Fig. 8 is a like view of a processed one ready to receive the webs;

Fig. 9 is a cross section on line 9-9 of Fig. '1.

The invention has been illustrated and described as used as anattachment on a milling machine on which the-metal frames of cross hairholders or reticles are quitegenerally grooved. While it is particularlyapplicable to that type of work, it is also applicable to a great manyother lines of work and capable of advantageous use in pratically. anycase in which it is desired to make surface cuts, fine grooves or thelike with accuracy, relative to a given point or line.

While stainless steel. is a preferred material for the attachment, itwill be readily understood that any other acceptable material may beused.

Preferably, though not essentially, the attachment is made. in severalparts detachably connected.

In order. to provide a fin or wall by which the attachment may besecurely clamped in a vise A, suchv as is regularly used with andaccompanies milling machines, a simple rectangular back plate I is.provided. Such a vise is mounted on the bed of the milling machine inusual and wellknown manner so. that it may be screw-fed laterally of thebed across the path of a work piece held in the clutch .of the dividerhead B or other corresponding part of the milling machine. To the backplate I is adjustably connected the piston receiving bar 2. Bar 2 isadjustably connected to back plate I by screws 3 and 4 playing innotches 5 and B, respectively. As will be seen, screw 3 is connectednear one end to bar 2 near its upper face, while screw 4 is connected tobar 2 near its opposlte'end and near its, lower face. In other words,the two screws are connected to the same face of bar 2 at diagonallyopposite points. While.v the screwsplay freely in notches 5 and 6 theirheads overlap the back plate I on the face remote from bar 2. So, bytightening screws 3 and 4, the bar 2 may be clamped immovably toplate 1. Likewise, by loosening one or both said screws, the bar 2 maybe tilted in one direction or the other, relatively to back plate I, andthen the screws 3 and 4 again tightened to clamp the bar in suchadjusted position on the plate." .This, of course, will raise or lowerthe cutting edge.

Bar 2 is bored longitudinally as at 1 so as to slidably receivetheplunger 8 of a forked piston 9 in which is rigidly though removablymounted a knife-edge cutting or scribing disc Ill, the setscrew'llpassing through one fork, the scribing tool hub and into theopposite fork. Plunger 8, slidably seated in "I is urged outwardly bycompression spring l2.v It may be held against outward movement by thelock bolt I3 threaded into the vertical bore l4 in bar 2 which boreintersects bore 1. The force of spring 12 may be varied by regulatingscrew I turned into the opposite end of bore I. With plunger 8 in fullyretracted position, as in Fig. 2, and screw I5 turned in only far enoughto engage it, the spring will not be under compression between screw I5and the end of plunger 8. Any further inward turning of I5 willcorrespondingly compress and add to the power of spring lg. This poweris, of course, transmitted to the scribing disc I0 so that it cutscorrespondingly deepit contacts.

plate I,is cutout as at I9.

To the bottom of bar 2 is removably screwed or otherwise attached abottom plate I6.. This plate extends at right angles to the back plate.Also, in assembled relation, theedge of I6 contacts the face of I and alateral cross section through the assembled'plates at any point on theirlength is substantially a T. On plate I6 is removably fixed by screws orthe like a second bar I! which acts as a spacer for bar 2 and a braceand guide for the forked piston 9, being parallel thereto throughout andin light contact therewith. At the same time, this'second bar I!provides material or base and foundation for a pair of levellingadjusting screws I8 which are threaded through bores in I"! and inaligned holes through plate I 6. These screws I8, it will be noticedpass through bar I! at short distances from its opposite ends andproject considerably below plate l6. By the use of screws I8, whenscrews 3 and 4 are loosened, the disc blade I0 of the tool may be movedto any desired operating position.

'The operation of the invention in use in a milling machine is asfollows:

Place a centering tool in the clutch of divider head B.

Line up the vise A on the bed C so that the plate I of the device, whenclamped inthe vise will place the scribing disc IIl approximately in thehorizontal plane of the centering tool in B. Clamp back plate I inplace, disposing it with its upper edge approximately horizontal. Theplunger 8 and forked piston 9 should be locked in retracted positionwith spring I2 under the desired compression. Screws 3 and 4 should bejust tight enough to hold the assembly together. Screws I 8 should beadjusted so that both engage the vise directly below. Preferably, theyshould be adjusted to bringplate I6 to approximately horizontal positionandin about the plane of the centering tool. Cutting disc I ll'will thenalso be substantially horizontal. Now loosen set screw [I to freeplunger 8 and disc I0 so that said disc I0 moves close to the tip of thecentering too Next, tip bar 2 by means of screws I8 longitudinally sothat the edge of cutting disc I0 exactly aligns with the, tip of thecentering tool.

In this alignment a magnifying glass may be used if desired for greateraccuracy. After this alignment has been completed and screws 3 and 4tightened to holding position, the plunger 8 should be fully retractedand locked by set screw I3. With parts thus adjusted, the vise isoperated to carry the attachment sufficiently to the rear to permitplacing the work piece in the chuck, the set screw I3 is loosened tofree plunger 8 and disc I!) and the vise is traveled forward,

carrying the disc across the work. In its passage across the work, discI0 will cut a fine straight line, diametrically across the work piece.The disc I0 is then retracted, the device moved to the 10 er lines orgrooves in the work piece with which T In order to provide ampleclearance for tool I I], in its retracted positionjback .4 rear again,the work rotated 90 degrees and the operation repeated. Where the metalframe of a reticle is the work piece, the two intersecting groovesprovide accurate seats for the spiderweb cross hairs. Where the surfaceis slightly rounded or convexed as at 2| instead of perfectly flat, thespring I2 will maintain the blade in continuous contact throughout itstravel regardless of the curvature.

The device may be easily, quickly and. very accurately set for extremelyprecise work. By repeated tests it has been found that a line made byabove setting checked exactly when the work was rotated 180 degrees, thesecond cut falling exactly in and accurately matching the first.

It will be noticed that the back plate is in contact with and braces thefork =9 as the tool is fed forward in making the cut.

Since the fork and tool project somewhat beyond the adjacent edge ofback plate I there could be considerable twisting strain thrown onplunger rod 8. However, bar I l on plate It, overlapping fork 9 engagesand braces it from the front and takes up all strain in that direction.These two engaging surfaces (front and back) prevent any lateralmovement of any nature of the tool I0, thoroughly assuring maintainedaccuracy and precision.

It will be noticed that by the adjustments provided, the lip of disc I 0may be accurately adjusted both as to the horizontal plane of thecutting disc and to offset and tendency to turn or tip about thelongitudinal axis of the plunger rod axis 8.

When. after considerable use, the cutting edge may become dulled, thedisc may be easily removed by loosening screw I I, resharpened andreturned. Or it may be removed, turned to present another part of theedge and remounted. One advantage of the circular edge is that it may berotated to successively present various portions without delaying toresharpen.

Where other types of machines are used, the

work piece should be centered similarly to centering in the divider headand the device of this invention should be mounted in a vise insubstantially the same position relative to the work piece and arrangedto travel the device in the same way as the vise on the milling machinetravels it. It-is needless to state that the attachment also, may bevery well used in many operations in which great precision is notrequired, regardless of the fact that it is of especial value in highprecision work.

Many changes may be made in the construction arrangement and dispositionof the various parts of the invention within the scope of the appendedclaims without departing from the field of the invention and it is meantto include all such within this application wherein only one preferredform has been illustrated, purely by way of example and with no thoughtor intent to, in any degree, limit the invention thereby.

Having thus described my invention, what I claim and desire to protectby Letters Patent 1s:

1. In a precision tool attachment, a supporting back plate, a bar, meansto adjustably clamp said bar to said back plate, a piston reciprocablymounted in said bar, a cutting element carried by said piston, a bottomplate carried by said bar, and means carried by said bottom plate fortilting said bar relative to said back plate.

2. In a precision tool attachment, a supporting back plate, a first bar,means to adjustably clamp said bar to said back plate, a pistonreciprocably mounted in said first bar and provided with a protrudingforked end, a cutting element sustained by said forked end, a bottomplate carried by said first bar, a second bar carried by said bottomplate and bracing said first bar, and means for tilting said first barrelative to said back plate.

3. In a precision tool attachment, a supporting back plate, a pistonreceiving bar, means to adjustably clamp said bar to said back plate, apiston movably mounted in said bar and carrying a cutting element, meansfor yieldingly urging said cutting element to operative position, abottom plate carried by said bar and means carried by said bottom platefor til-ting said bar relative to said back plate.

4. In a precision scribing tool attachment, a supporting back plate, apiston receiving bar, means to adjustably clamp said bar to said backplate, a piston movably mounted in said bar and carrying a cuttingelement, means for yieldingly urging said cutting element to operativeposition, means for locking said element against movement, a bottomplate carried by said piston receiving bar and means carried by saidbottom plate for tilting said bar relative to said back plate.

5. In a precision scribing instrument attachment, a supporting backplate, a piston receiving bar, means to adjustably clamp said bar tosaid back plate, a piston movably mounted in said bar and carrying a.cuttin element tool, means for yieldingly urging said cutting element tooperative position, means for regulating said urging means, a bottomplate carried by said piston receiving bar and means carried by saidbottom plate for tilting said bar relative to said back plate.

6. A precision scribing instrument attachment comprising a firstsupporting back plate having more than one transverse slot, a pistonreceiving bar, screw means to adjustably clamp said piston receiving barto said back plate through said transverse slots, 3, piston reciprocallymounted in said piston receiving bar, said piston having a protrudingyoked end, a cutting tool moveably mounted in said yoked end, means forlocking said cutting tool against movement, spring means mounted in saidpiston receiving bar and in contact with said piston for yieldinglyurging said cutting tool to an operative position, means mounted to locksaid piston against movement, means for regulating said spring means, abottom plate attached to said piston receiving bar, a bracing barmounted on said bottom plate to brace said piston laterally and screwmeans threaded thru said bar and second plate for positioning saidcutting tool.

7. A precision scribing tool comprising an elongated first plateprovided With at least two transverse slots, a first bar in slidablecontact with said first plate and provided with a longitudinal bore, tworeleasable screws extending through said slots and engaging said firstbar to lock said first bar to said first plate in any desired operatingposition to which it is slid, a piston extending partly into said boreand slidable therein, said piston being in slidable contact with saidfirst plate, a scribing element sustained by said piston, adjustablespring means to urge said piston longitudinally, a second plate securedto said first bar and substantially perpendicular to said first plateand in slidable contact with said piston, a second bar secured to saidsecond plate and substantially parallel to said first plate and inslidable contact with said piston, and two screws substantially parallelto said first plate to support said first bar during slidable adjustmentthereof, whereby said first and second plates and said second bar assistin guiding and bracing said piston during operation of said tool.

ROBERT S. THOMPSON.

No references cited.

